Test leak unit

ABSTRACT

A test leak unit ( 1 ) includes a supply of test gas, preferably helium, and an element ( 14 ) for determining leakage rates. The aim of the invention is to create a simple, robust and easily refilled test leak unit, especially for detecting packaging leaks. To this end, the test gas supply is stored under substantially atmospheric pressure in a resealable reservoir ( 2 ) including a closing part ( 3 ), such that when the reservoir ( 2 ) is closed, a test gas-impermeable seal is developed between the closing part ( 3 ) and the reservoir ( 2 ), and the leakage rate-determining element ( 14 ) forms part of the closing part ( 3 ).

BACKGROUND OF THE INVENTION

The present invention relates to a test leak unit comprising a supply oftest gas, preferably helium, and an element for determining leakagerates.

In leak testing of hollow bodies, the method of vacuum test gas leakagedetection has prevailed. The wall of the hollow body is exposed to adifferential¹⁾ pressure produced by evacuating the hollow body or itssurroundings. Test gas, commonly helium, admitted on the side at thehigher pressure, penetrates possibly present leaks and is recorded by atest gas detector, for example, a mass spectrometer, connected on theside at the lower pressure.

¹⁾ Translator's note: “The German text states “Differendruck” herewhereas “Differenzdruck” would be appropriate. Therefore“Differenzdruck” has been assumed for the translation.

Test leak units of the aforementioned kind are, for example, known fromDE-A documents 32 43 752 and 36 13 694. These supply a leakage of knownproperties and serve the purpose of calibrating leak searchinginstruments. To this end, they are connected via connecting lines to theleak searching instrument in which a test gas detector is located.

Frequently, such test leak units are built into the leak searchinginstrument. An other possibility of checking the operation of the leaksearching instrument is to hold the test leak unit with its opening,through which the test gas flows out via a leakage rate determiningelement, in the vicinity of the inlet of the leak searching instrument.The test gas arriving at the test gas detector will then produce thedesired test signals.

From WO 98/16809 a process and a device for testing the leak tightnessof packages is known. Located within the sealed package is the test gas(preferably helium, also nitrogen, argon, carbon monoxide, halogen gasesor the like). The leakage test is performed within a test chamberconsisting of foils. For a process and a device of this kind, a teststep has already been proposed improving the reliability of the leakagetest. This proposal is such that the wall of a unit under test isprovided with a leak and that the leak searching process be done withthis unit under test itself. Thus one of the units under test itself isbeing used as the test leak unit. However, checking of a leak searchinginstrument with a “quasi test leak” of this kind is only possiblequalitatively. The magnitude of the leakage produced by piercing isunknown. This equally applied to the concentration of the test gaswithin the unit under test, which above all may have changed, if theselected unit under test for the “quasi test leak” already had a leakagebefore.

SUMMARY OF THE INVENTION

It is the task of the present invention to create a simple, robust, andeasily refilled test leak unit which is also suited for packaging leaksearching instruments.

This task is solved by the present invention in the case of a test leakunit of the aforementioned kind, by storing the test gas reservoirsubstantially under atmospheric pressure in a resealable reservoir witha closing part, where with the reservoir sealed, test gas tight sealingmeans are provided between closing part and reservoir and where theleakage rate determining element forms part of the closing part.

Since the pressure in the test gas reservoir is approximately atatmospheric pressure, test gas flows out through the leakage ratedetermining element only when the test leak unit is placed in a vacuumchamber, i.e. in a leak searching chamber in which the units under testare subjected to a vacuum leakage test. Without a significant change inthe concentration of the test gas in the reservoir, many test cycles(for a reservoir of 0.25 liters and helium as the test gas about 10,000)can be run. The fact that the filling pressure in the test leak unitcorresponds to the surrounding atmospheric pressure, offers the addedbenefit that refilling the test leak unit may be performed simply withthe aid of a spray gun. An otherwise necessary gas lock is no longerrequired. Spraying of the test gas into the reservoir has the effect ofcausing the previously used filling to flow out. In all, relativelylarge leakage rates may be attained with the test leak unit according tothe present invention over a long period of time. In the case of theotherwise common internal pressure far above atmospheric pressure ofknown test leak units, the reduction in pressure will rapidly cause achange in the leakage rate.

The adaptation of the leakage rate of the test leak unit according tothe present invention to the specific process of the customer, may besimply performed by selecting a closing part with the desired leakagerate. If the specific requirements of the customer change, this closingpart may be exchanged quickly and simply by a closing part having adifferent leakage rate.

It is important, that when employing a test leak unit according to thepresent invention in the vacuum of a leak searching chamber, the testgas will flow out exclusively through the leakage rate determiningelement. Any further seal, be it the seal between closing part andreservoir or a seal between the leakage rate determining element and theclosing part, must provide a tight seal against the test gas. Whenemploying helium as the test gas, PU seals must be used, preferably“Platilon” (company Atochem, Bonn).

A screwed plug preferably serves as the seal between closing part andreservoir. Compared to other closing means (bayonet catch, for example)the desired level of leak tightness against the test gas can be attainedparticularly well.

Further advantages and details of the present invention shall beexplained with reference to the design examples depicted in the drawingswherein:

FIG. 1 is a partial side elevation with portions uploaded awayillustrating a first embodiment of the invention; and

FIG. 2 is a partial side elevation similar to FIG. 1 illustrating asecond embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Depicted in drawing FIGS. 1 and 2 is each a test leak unit 1 with areservoir 2 and a closing part 3. The closing part 3 has a section 4with an outside thread 5. Assigned to this outside thread 5 is an insidethread 7 in the neck 6 of the reservoir 2.

A further section 8 of the closing part 3 has, compared to the section 4an increased diameter. Its rim is provided with a recess 9 facing thereservoir 2, said recess accepting a sealing ring 11. With the closingpart 3 fully screwed into the neck 6 of reservoir 2, the upper rim ofthe neck 6 is in contact with the sealing ring 11 thereby ensuring thedesired degree of leak tightness for reservoir 2.

In both drawing figures the leakage rate determining element isdesignated as 14. It consists of a quartz capillary 15, which ispreferably embraced by a plastic jacket. It is affixed in a holder 16designed like a spray nozzle with thread 17 and sealing ring 18 (drawingFIG. 2). Elements of this kind are basically known from WO 95/21373.

In the design example according to drawing FIG. 1, the holder 16 isdirectly screwed into an axial bore 19 in the closing part 3 in such amanner that the capillary 15 penetrates said bore 19 and is linked tothe internal chamber of the reservoir 2. In the design example accordingto drawing FIG. 2 an insert 21 is provided which is cemented in a testgas tight manner into the axial bore 19. Holder 16 is screwable into theinsert 21. Part of the insert 21 is a protection tube 22 which surroundsthe capillary 15 in its built-in state.

Finally the closing part 3 is equipped with channels 24, 25 serving thepurpose of admitting fresh test gas and discharging the gas mixturestill present in reservoir 2. Said channels have outer openings 27 and28 respectively located on the side in section 4 of the closing part 3and arranged in such a manner that they are accessible when the closingpart 3 is partly screwed out of the reservoir 2 (drawing FIG. 2). A tubesection 29 follows at the inner opening of the test gas supply channel24, said tube section extending into the bottom section of the reservoir2. This ensures that fed in fresh test gas will cause the gas mixturestill present in the reservoir 2 to flow out of the discharge channel25. During filling, the container is preferably placed upside down sothat the in flow of lighter helium gas displaces the old gas mixtureresp. air down and out.

In the design example according to drawing FIG. 1, the supply anddischarge channels 24, 25 are formed by axial bores. These open out intoradial bores 31, 32 which form the outer openings.

In the design example according to drawing FIG. 2, the bore 19, which issealed towards the outside by cemented in insert 21, serves the purposeof a supply channel 24 for the supply of fresh test gas. The dischargechannel is created by closing part 3 being flattened at the side withinthe area of its section 4.

What is claimed is:
 1. A test leak unit comprising: a helium test gasreservoir; a reclosable reservoir vessel, said reservoir vessel having aclosure piece; a leakage rate-determining element; and a testgas-impermeable sealing means disposed between said closure piece andsaid reservoir vessel when said reservoir vessel is closed, said testgas reservoir being maintained substantially at atmospheric pressure insaid reclosable reservoir vessel and said leakage rate-determiningelement being a component of said closure piece, said closure piecebeing equipped with inflow and outflow channels to permit replenishmentof said vessel with new test gas.
 2. A leak test unit according to claim1, wherein the closure between the reservoir vessel and the closurepiece is developed as a screw connection.
 3. A leak test unit accordingto claim 2, wherein outer terminations of the inflow and outflowchannels are disposed laterally on said closure piece, such that saidchannels are closed when the reservoir vessel is closed.
 4. A leak testunit according to claim 1, including a tube section extending into thelower portion of the reservoir vessel, said tube section adjoining aninner termination of the inflow channel.
 5. A leak test unit accordingto claim 1, wherein said closure piece includes a bore, said leakagerate-determining element being accommodated in said bore.
 6. A leak testunit according to claim 5, wherein said leakage rate-determining elementis comprised of a quartz capillary sheathed in a synthetic jacket, saidelement being secured within a mounting and resembling a spray-nozzle.7. A leak test unit according to claim 6, wherein said mounting isscrewed into the bore of said closure piece.
 8. A leak test unitaccording to claim 5, including an insert disposed within said bore intowhich said leakage rate-determining element can be screwed.
 9. A leaktest unit according to claim 6, including a protective tube provided forthe quartz capillary of the leakage rate-determining element.
 10. A leaktest unit according to claim 1, wherein said closure piece includes arecess for a sealing ring, said sealing ring being in contact with anupper edge of a neck of the reservoir vessel after said vessel has beenclosed.